Light can be used to treat a wide variety of diseases. When light alone is used to treat a disease, the treatment is referred to as phototherapy. Light may be used in conjunction with a pharmaceutical in which case the treatment is called photodynamic therapy (PDT). These therapies can be used to treat a variety of skin and internal diseases. In PDT, a light-sensitive therapeutic agent known as a photopharmaceutical is supplied externally or internally to an area of the body which is to be treated. That area is then exposed to light of a suitable frequency and intensity to activate the photopharmaceutical. A variety of photopharmaceutical agents are currently available. For example there are topical agents such as 5-aminolevulinic acid hydrochloride (Crawford Pharmaceuticals), methylaminolevulinic acid (Metfix®, Photocure). There are also injectable drugs used primarily for internal malignancies, including Photofin® (from Axcan) and Foscan® (from Biolitech Ltd). Often, the drug is applied in a non-active form that is metabolised to a light-sensitive photopharmaceutical.
In photodynamic therapy, the primary technique for supplying light to the photopharmaceutical is to project light of a suitable wavelength from standalone light sources such as lasers or filtered arc lamps. These sources are cumbersome and expensive, and are therefore only suitable for use in hospitals. This leads to inconvenience for the patient, and high cost for the treatment. High light irradiances are needed in order to treat an acceptable number of patients per day (for the treatment to be cost effective) and to avoid unduly inconveniencing the patient.
WO 98/46130 (Chen and Wiscombe) discloses arrays of LEDs for use in photodynamic therapy. The small LED sources taught therein result in uneven light incident on the patient. Fabrication of arrays is complicated because of the large number of connections required. The devices shown therein are designed for hospital treatment.
GB 2360461 (Whitehirst) discloses a flexible garment which uses a conventional photodynamic therapy light source to produce light which is then transmitted through optical fibres. As such light sources are heavy, the device is not ambulatory and is limited to hospital use.
U.S. Pat. No. 5,698,866 (Doiron et al) discloses a light source using over-driven inorganic LEDs. The resulting light output is not even. A heat-sinking mechanism is required, and the device is suitable only for hospital treatment.
WO 93/21842 (Bower et al) disclose light sources using inorganic LEDs. Although transportable, the device is not suitable for ambulatory use by a patient at home and clinical treatment is envisaged.
A further problem with existing approaches is that it can be difficult to achieve uniform illumination with such sources, especially on curved body parts.